Method and device for respiratory monitoring

ABSTRACT

A respiration monitoring system has deformation transducers on a flexible substrate arranged to adhere to a patient&#39;s torso. A processor receives signals in channels from the transducers and processes them to eliminate, reduce or compensate for noise arising from patient motion artefacts, to provide an output representative of respiration. The transducers have a size and a mutual location on the substrate so that a first transducer can overlie at least part of the 10th rib and a second transducer can overlie at least part of the 11th rib or the abdomen, and the processor processes data from the first transducer as being primarily representative of rib distending respiration and from the second transducer as being primarily representative of either diaphragm respiration or patient motion artefacts.

INTRODUCTION Field of the Invention

The invention relates generally to devices useful in measuring andmonitoring respiratory events in a human subject.

Prior Art Discussion

Respiratory rate is the measure of the number of breaths a person hasper minute and is a key vital sign in human subjects. Spirometry is themeasure of lung capacity or lung volume in a human subject.Deterioration of these respiratory functions is the decline or increaseof these measures. Measurements outside, or approaching the boundariesof the predetermined physiological normal values are a pre-indicator toharmful and fatal emerging ailments in human subjects.

Respiration is the process by which living organisms take in oxygen andconvert it to energy. Part of this process is the mechanical inhalationof air which, for humans, is done via the nose and mouth. The mechanicalrespiratory effort is produced by the muscles of respiration. Thesemuscles aid in bath inspiration and expiration. The muscle groups whichmake up this collection include the diaphragm, external intercostal, andinternal intercostal muscles. This process is known as respiratoryeffort, and it is enabled by either or both of:

-   -   a) The partial or total displacing of the rig cage (hereafter        referred to as rib breathing) upwards and outwards by the        external and internal intercostal muscles, along a fixed locus,        to produce a vacuum inside the thoracic cavity, thus drawing air        into the lungs to enabling respiration to occur,    -   b) The diaphragm pushing down into the abdominal region        (hereafter referred to as diaphragm breathing) forcing the        abdominal organs to distend outward and thus producing a vacuum        in the thoracic region by increasing the volume in the abdominal        region.

The above movements may be referred to as distending the rib cage.

A reason for the respiratory rate or capacity of the lung of a patientto fluctuate over a period of time, where physical activity is notconsidered, can be the result of physiological changes in the health ofthe patient. Infections in the body can result in a fever and higherheart rate. An infection also produces an increase in respiratoryeffort, and could be viral or bacterial, or as a result of theenvironment or complications resulting from medication or surgery.Pneumonia, chronic obstructive pulmonary disease (COPD), and sepsis areall ailments representative of the above and can be indicated byfluctuating respiratory function. This may express either as analteration of the respiratory rate of the patient or the capacity of thepatient to draw in air for efficient respiration.

Respiratory rate is a predominant metric in a predicative patientscoring system known as the Early Warning Score (EWS). Chronic patientssuffering from lung diseases such as COPD can be monitored over longperiods of time by measuring their lung capacity. As lung diseasesaffect the normal mechanical operation of respiratory effort, measuringthe ability of patients to breathe deeply is also a key measure of theirdeterioration or recovery. The comprehensive measure of respiratoryrates enables medical staff to better assess the EWS with high accuracyand intervene sooner.

US2012/0296221 (Philips) describes a method and apparatus fordetermining a respiration signal. A single multi-axial accelerometer ispositioned on the body. WO2009/074928 (Philips) describes use of ECGelectrodes on an elastically deformable bridge, and there is also astrain sensor and an accelerometer.

The invention is directed towards providing a system for respiratorymonitoring which is simpler and/or more robust, and/or more reliablethan the prior art.

SUMMARY OF THE INVENTION

According to the invention, there is provided a respiration monitoringsystem comprising:

-   -   a plurality of deformation transducers on a flexible substrate        arranged to adhere to a patient's torso, and    -   a processor adapted to receive signals from said transducers and        to process them to eliminate, reduce, or compensate for noise        arising from patient motion artefacts, to provide an output        representative of respiration.

In one embodiment, the deformation transducers are elongate and arearranged on the substrate at a mutual acute angle. Preferably, the angleis in the range of 20° to 80°, preferably 25° to 40°, and mostpreferably in the region of 27° to 33°.

In one embodiment, the transducers have a size and a mutual location onthe substrate so that a first transducer can overlie at least part ofthe 10^(th) rib and a second transducer can overlie at least part of the11^(th) rib or the abdomen, and the processor is adapted to process datafrom the first transducer as being primarily representative of ribdistending respiration and from the second transducer as being primarilyrepresentative of either diaphragm respiration or patient motionartefacts. Preferably, the deformation transducers are positioned at anacute angle to each other on the substrate, and the processor is adaptedto process data from the transducers on the basis that an apex definedby said mutual position is pointed rearwardly and downwardly withrespect to a human subject.

In one embodiment, the system further comprises an accelerometer. In oneembodiment, the processor is adapted to process an accelerometer outputby correlating the degree of motion artefacts with bodily displacementfor aiding the process of eliminating motion artefacts and detectcyclical movements.

In one embodiment, the system includes a gyroscope. Preferably, theprocessor is adapted to process a gyroscope output by enabling theposture of the body to be known to the processor, thus enablinganomalies of the transducers to be accounted for.

In one embodiment, the system comprises a unitary sensor for adhering toa patient's skin, said sensor including the substrate with thedeformation transducers, and the processor. In one embodiment, theprocessor is included in a housing on the substrate with a signalconditioning circuit. Preferably, the processor housing is releasablymounted on the substrate.

n one embodiment, the processor is adapted to communicate wirelessly viaan interface to a host processor.

In one embodiment, the deformation transducers include at least twostrain transducers. In one embodiment, in the strain transducers arepiezoelectric transducers.

In one embodiment, the processor is adapted to detect excessivedisplacements resulting in over-pressurisation from invasive ornon-invasive artificial ventilation machines.

In one embodiment, the processor is adapted to perform signalconditioning by baseline subtraction against an input voltage signalfrom the transducers, and to further condition the signal using anexponential moving average filter.

In one embodiment, the processor is adapted to trigger an artefactdetection algorithm at regular intervals in which signals which areoutside the limits of measurement are removed.

In one embodiment, the processor is adapted to execute a time domainalgorithm when determining respiration rate.

In one embodiment, the processor is adapted to execute a frequencydomain algorithm when determining respiration rate. Preferably, the timedomain algorithm checks distances between peaks and troughs in arespirator waveform and derives a respiration rate. In one embodiment,the frequency domain algorithm uses a fast Fourier transform to extractfrequency domain information. In one embodiment, the sensor includes anaccelerometer and the processor is adapted to execute the frequencydomain algorithm to take accelerometer data as a secondary input and tocompensate for cyclical interference from the subject or environmentsuch as walking, by extracting frequency domain information from theaccelerometer.

In one embodiment, the processor is adapted to detect and compensate forlarge movements using the accelerometer data.

In one embodiment, the processor is adapted to assume that a deformationwaveform is represented by a repeating pattern of peaks and troughs at arate indicative of the respiratory rate of the subject, and magnitude ofa received transducer signal is considered only of importance if saidsignal becomes so large as to exceed an output limit of the sensor, orso small as to become indistinguishable from noise.

In one embodiment, the processor is adapted to detect apnea events insleeping subjects. Preferably, the processor is adapted to recognizemissing breathing signals as representative of apnea.

In one embodiment, the system further comprises a wireless transceiverand the processor is adapted to transmit to an external device data todisplay a respiratory rate history of a subject.

In one embodiment, the processor is adapted to receive a uniqueidentifier for a use with a particular subject, and to discontinue orerase said identifier upon removal and/or re-charging for a next use. Inone embodiment, the processor is adapted to save a scanned MedicalRecord Number (MRN) as a unique identifier. In one embodiment, theprocessor is adapted to automatically apply a temporary identifier uponremoval or re-charging.

In another aspect, the invention provides a method of monitoringrespiration of a human subject using a system comprising:

-   -   a plurality of deformation transducers on a flexible substrate        arranged to adhere to a patient's torso, and    -   a processor adapted to receive signals from said transducers and        to process them to eliminate, reduce, or compensate for noise        arising from patient motion artefacts, to provide an output        representative of respiration,

-   the method comprising the steps of adhering the substrate to a human    subject and the processor processing signals from the transducers to    derive an output representative of respiration of the human subject.

In one embodiment, the substrate is placed so that a first transducersubstantially overlies a 10^(th) rib and a second transducer overlies afloating rib or the abdomen, and the processor monitors signals fromsaid transducers by treating signals arising from deformation of thefirst transducer as being representative of rib distending respirationand by treating signals arising from deformation of the secondtransducer as being representative of diaphragm breathing or anon-respiration artefact.

In one embodiment, the processor automatically decides on what thedeformation of the second transducer represents according to a signalfrom an auxiliary sensing device.

In one embodiment, the auxiliary sensing device is an accelerometer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of some embodiments thereof, given by way of example onlywith reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a sensor of a system of the invention,

FIG. 2 is an exploded view of a re-usable part,

FIG. 3 is a set of views of layers of the transducers, and

FIG. 4 is an exploded perspective view of the layers of the sensor'ssubstrate,

FIG. 5 is a diagram showing an optimal position for sensor on the body;

FIG. 6 is a Hock diagram of the sensor system;

FIG. 7 shows an instrumental amplifier circuit to create a highcommon-mode resection and high gain to eliminate any mutual environmentinterference and boost the signal for processing respectively for asingle transducer;

FIG. 8 shows low pass filtering circuitry to produce a single output(per sensor) for digital signal processing, with high frequencycomponents removed, for a single transducer embodiment;

FIG. 9 is a flowchart outlining an algorithm used to process the sensoroutputs to generate a respiratory rate;

FIG. 10 is a flowchart detailing the use of a Fast Fourier Transform aspart of the algorithm in FIG. 9;

FIG. 11 is a flowchart detailing the use of a time domain algorithm aspart of the algorithm in FIG. 9;

FIGS. 12(a) to 12(f) are plots, having a normalised numerical verticalaxis and a time horizontal axis, showing various transducer and systemsignals as follows:

-   -   FIG. 12(a) shows the raw output from a single transducer over a        60 s time period showing the peaks and troughs indicative of        normal breathing, in which one movement artefact can be seen as        an increase in the signal strength,    -   FIG. 12(b) shows the same signal with baseline correction and        smoothing applied,    -   FIG. 12(c) shows the results from an artefact detection        function,    -   FIG. 12(d) shows the same signal with the section designated as        artefact smoothly removed from the waveform.    -   FIG. 12(e) shows the signal in FIG. 12(d) with peaks and troughs        identified by the system's processor, and    -   FIG. 12(f) shows the frequency spectrum of the signal, with the        most prominent signal highlighted at approximately 0.25 Hz, or        15 breaths per minute;

FIG. 13(a) shows signals for each channel representative of normalbreathing over a 60 s period which has minimal movement artefact whilethe subject is standing, and FIG. 13(b) shows the corresponding signalwhen the subject is lying on their back, again having a normalisednumerical vertical axis and a time horizontal axis; and

FIG. 14(a) shows the signals from transducers over a period of 1 hour,collected when the subject was asleep. FIG. 14(b) shows the signals froman accelerometer housed in the electronics housing for the same period,again having a normalised numerical vertical axis and a time horizontalaxis.

DESCRIPTION OF THE EMBODIMENTS

Referring to FIGS. 1 and 2 a monitoring system comprises a sensor I witha disposable substrate 2 for adhering to a patient torso and a re-usableelectronics controller 3 adhered to the substrate 2. The substrate 2comprises a body 4 within which are embedded elongate transducers 5 and6 for measuring deformation. These are linked by conductors 7 to thecontroller 3. A sensor system includes the sensor 1 and also a hostprocessor linked by cable or wirelessly, and this may in turncommunicate with a remote server.

The controller 3 comprises a plastics housing with a top part 10 and abase 11, containing a circuit board 12 and a rechargeable battery 13,and an alarm sounder 14. There is a connector 15 for wired connection toan external device or host system, although the circuit 12 is alsoBluetooth enabled for wireless communication with such a device orsystem.

The controller 3 is mechanically joined to the substrate 2 by use of anindustrial grade hook and loop fastener with the hook side on the sideof the controller 3 and the loop side on the consumable substrate 2.This construction allows for durable attachment of the device. Itfurther allows removal of these two elements which is useful in amedical application where consumable body contact sensors are desired tobe for single patient single use.

Referring in particular to FIG. 3 the transducers 5 and 6 comprise apiezoelectric film 5(a), 6(a) sandwiched between:

-   -   a coating ink pattern 5(b), 6(b) and a positive ink pattern        5(c), 6(c), on top; and    -   a negative ink pattern 5(d), 6(d) and a Mylar layer 5(e), 6(e)        underneath.

The composition of the transducer is therefore a multi-layer piezo stackseparated by a metal foil. In this embodiment the piezo stack is amulti-purpose, piezoelectric transducer for detecting physical phenomenasuch as vibration or impact or general deformation. The piezo filmelement is laminated to the sheet 5(e) of polyester (Mylar), andproduces a useable electrical signal output when forces are applied tothe sensing area.

This compositional stack is heat-laminated using a translucent polymer.Each piezo film layer is partially extended to form a terminal by whicha clamp is fixed to. This provides a secure electrical contact for theinstrumentation amplifier circuitry.

The substrate body 4 is shown in most detail in FIG. 4. It comprisespolypropylene clear release film 4(a), 3M™ medical grade siliconeadhesive 4(b), and a polyester layer 4(c). The transducers 5 and 6 arelocated between the adhesive 4(b) and the polyester 4(c) layers.

As shown in FIG. 5, the sensor may in one embodiment be placed so thatthe top transducer 5 is over the 10^(th) rib, which is the lowermostfixed rib. This leaves the lower transducer 6 in the vicinity of the11^(th) rib, which is floating. Thus, the transducer 6 is effectivelyover the abdomen and is not affected by the ribs. This is described inmore detail below.

Referring to FIG. 6, at a block diagram level the sensor 1 comprises thetransducers 5 and 6 feeding a filtering circuit 20, and an ADC (notshown) feeds a Bluetooth module 24. There is a DSP processor 21 alsolinked with the Bluetooth module 25. A battery management circuit 22 islinked with the battery 13, and there battery charging terminal 23. Thecontroller 3 houses an accelerometer 25, and there are LED and alarmsounder output devices 26 and 27.

The two transducers 5 and 6 are of equal length, width, thickness, andcomposition. They are positioned 30° apart from one another about asingle point of common placement which ensures a preferred form factor.This preferred configuration is not the only configuration at which thisinvention will be effective. The angle between each transducer can bedifferent and indeed they may be parallel. However the preferred rangeis 25° to 55°, and the most preferred is in the region of 27° to 33°.The preferred length and width of each transducer is in the range of 30mm to 50 mm and 50-400 μm thick.

The transducers 5 and 6 provide the deformation information as describedbelow to allow the processor 21 to automatically generate an outputindicating patient respiration. However, the accelerometer 25 allowsimproved effectiveness in analysing signals arising from wearer'sactivity and posture. Such variables of posture and activity have directinfluence upon the effectiveness of the system. The system can alsoidentify how quickly the human subject is moving, and the subject'sposture and when movement based artefacts have been induced in thestrain transducer signal. This further enables the human subject to livea normal functional life while the device comprehensively measures therespiratory performance without imposing

The sensor 1 may be positioned for example over the 9^(th) to 11^(th)rib, with the controller 3 approximately situated under the subject'sarm. The vertical position is determined with reference to the subject's10^(th) rib, with the transducer 5 being preferably situated on or justbelow the 10^(th) rib and in line with this rib. The transducer 6 wouldtherefore be adhered to the subject's abdomen. The transducer 6 ispreferably horizontal, but subject physiology may require the transducer6 to be placed at an angle. The apex of the angle should point towardsthe rear of the subject. FIG. 5 shows the sensor 1 mounted on thepatient's skin at one side. However, the sensor could alternatively beon the opposite side in a mirror-image fashion.

The transducer 5 is particularly responsive to a distending movement ofthe rib cage, forwardly and laterally. This is almost entirely due torespiration. There may also be pivoting out of the plane of the page inFIG. 5, primarily due to motion artefacts such a walking. Importantly,the transducer 5 is approximately equally responsive to rib distendingand motion artefacts, whereas the transducer 6 is less responsive to ribdistending and equally responsive to the motion artefacts. When thesubject changes their posture, and/or begins breathing under a differentregime (normally chest breathing or diaphragm breathing) the signalexpressed on the transducers 5 and 6 can change greatly. Typically thetransducer 5 which is resting on the rib responds with greater magnitudewhen the subject is upright and/or breathing mostly using chestmovements. When the subject is lying and/or diaphragm breathing thetransducer 6, resting on the abdomen, typically responds more strongly.In atypical cases, for instance when the subject is breathing heavilyusing the ribs, the respiratory response from a transducer can be ofsuch small magnitude as to be indistinguishable from background noise.In this event, the data from this transducer or 6 is discarded, and theother transducer is used solely to derive the respiratory rate.

Different subjects show different signals on transducers for the sameposture due tai emphasis on gut or rib breathing, and variations inplacement. It is not possible to guarantee the patient's position withtransducers. The accelerometer 25 helps to determine the orientation ofthe patient, and the processor compensates the transducer outputsaccording to information from the accelerometer 25.

The system may be used for monitoring respiratory performances in aclinical environment, or alternatively in a non-clinical environmentsuch as physical exercise monitoring for sports performance enhancement.

The system may be used for the monitoring of apnea events in sleepingsubjects. Small configuration changes to the sensor will allow for apneamonitoring. Examples of such alterations include algorithm emphasis ondetecting missing breathing signals, or modification of the software toproduce a waveform for use in diagnosis by a medical professional.

Regarding data processing and communication, in one configuration, theBluetooth (BT) module 24 is replaced with a removable hard disk. Inanother configuration the BT module 24 constantly streams the breathingwaveforms, and processing is carried out on a desktop PC or othercomputer. In instances where healthcare professionals wish to monitorthe produced signals directly, limited algorithms can be implemented toclean up the respiratory signal for presentation.

A Bluetooth module 24 is used to communicate with an external device todisplay the respiratory rate history of the wearer. To ensure continuityof service, on attachment, the BT module is renamed with the patient'sMedical Record Number (MRN), for example as scanned from a patientrecords barcode. The renaming is temporary and lasts for the duration ofthe device attachment to the patient. Upon removal or recharging, the BTmodule is automatically renamed to its default identifier. The renamingof the BT module 24 with the MRN allows any authorised device tointeract with the sensor 1 for the duration it is attached to thepatient.

In instances where the patient can be assumed to be in a steady positione.g. short time spent lying down, signals from a single transducer cansuffice to record respiratory rate. However, the multi-transducerconfiguration covers the full spectrum of patient postures andrib/diaphragm breathing.

In more detail, the signals from both transducers 5 and 6 are filteredand the signal is processed to extrapolate the true wanted signal. Thisarrangement achieves both filtering and analytical processing capabilityat the point of measurement. It achieves this with very littlerestriction in patient movement. Also, some of the components, such asthe signal conditioning circuits 20 and the processor 21 are local onthe sensor 1. Such a sensor can also be more robust in terms of itsapplication to different physiological parameters e.g. body mass index,body position, location, activity and/or similar parameters. Theinclusion of the accelerometer 25 in the device allows such well knownart as fall detection, step detection and orientation monitoring to beeasily incorporated into the sensor 1. The preferred location for anaccelerometer is in the reusable electronic circuitry unit, preferablyintegrated into the processing circuit 16. The exact placement of theaccelerometer is of little importance, as the accelerometer is used todetect gross movement of the subject's body.

The sensor 1 does not have electrical wires which might interfere withthe patient. Also, the sensor 1 has a low-profile construction so asriot to interfere with the natural movement of the arms of the patient,with an ergonomically efficient design. The sensor is designed to bewearable for a period of up to 8 days. During this period, the devicecontinuously collects and processes data from the transducers and wheninterrogated by the supervising medical professional report on thesubjects respiratory rate over the proceeding number of hours.

FIG. 7 shows an instrumentation amplifier which amplifies the signalsarriving from a single transducer for later processing.

FIG. 8 shows a difference amplifier followed by a 2^(nd) order low passfilter. The difference amplifier removes the reference voltage from theincoming signals and amplifies the signal by a gain of one. The low passfilter removes higher frequency signals from the sensor signal.

The signal processing of the outputs of the movement transducers 5 and 6and the accelerometer 25 is explained in more detail in FIGS. 9, 10 and11. The plots of FIGS. 12(a) to 12(e) are generated at the blocks inFIG. 9 as indicated. Sensor inputs are connected into the microprocessorwhere all digital analytics are calculated. At this stage digital signalconditioning is performed. This is required supplementary to analoguefiltering so as to reduce the effect of abasing and spurious noise.Filtering in the digital domain provides a richer and more versatilefiltering process than what can be achieved in the analogue domain.

Once acquired, the incoming signals are processed to calculate therespiratory rate of the subject over a given time period. Several mainalgorithm steps are used for the reliable calculation of rates in thepresence of movement or other artefacts; signal conditioning, artefactdetection, artefact resolution, respiration rate derivation, as well asother miscellaneous supporting algorithms. Rate detection algorithmswere noted to fall into two main categories; time domain analysis andfrequency domain analysis. Time domain analysis includes techniques suchas peak and trough detection, template matching and machine learning.Frequency domain analysis includes techniques such as the discreteFourier transform, wavelet analysis and auto- and cross-correlationtechniques. Algorithms can include inputs from the on-boardaccelerometer or gyroscope.

One implementation of an analysis algorithm is outlined in FIG. 9. Thisimplementation is given by way of example only, and does not limit theinvention to the use of other algorithms, or sub-algorithms. Thisalgorithm is optimised for low power consumption and uses theaccelerometer 25 data in addition to the deformation transducers 5 and 6to derive a clean, conditioned respiratory rate. Signal conditioning iscarried out by baseline subtraction against the input voltage signal.The signal is further conditioned using an exponential moving averagefilter to smooth the signal. When the algorithm is triggered, every 25s, an artefact detection protocol is triggered. Artefacts detected onthe piezoelectric transducer signal (for example, signals which are‘railing’, or outside the limits of measurement) are them removed fromthe signal by smoothly bringing the signal to zero in these areas. Twoseparate respiratory rate algorithms are then run—one a time domainalgorithm and one a frequency domain algorithm. The first concentrateson looking at the distance between the peaks and troughs in therespirator waveform and deriving a rate for that. This is outlined inFIG. 11. The second uses a fast Fourier transform to extract frequencydomain information from the waveform, shown in FIG. 10. This algorithmalso takes the accelerometer data as a secondary input. Cyclicalinterference from the subject or environment, e.g. walking, iscompensated for by extracting frequency information from theaccelerometer. Large movements are also detected and compensated forusing the accelerometer data. Once the rate calculations are made, theextracted rates are buffered for communication via Bluetooth to anexternal tablet PC.

Signals output from the sensor transducers differ greatly from subjectto subject and when changes in posture or breathing regime occur. Thisincludes changes in signal strength, changes in the shape of therepeated breathing pattern, and the relative strength of the signalsfrom each of the strain transducers. The implemented algorithm onlyassumes that the respiratory signal is represented by a repeatingpattern of peaks and troughs at a rate indicative of the respiratoryrate of the subject, as shown in FIGS. 12 and 13 and 8. The magnitude ofthe sensor output is considered only of importance if the signal becomesso large as to exceed the output limit of the sensor, or so small as tobecome indistinguishable from noise. The shape of the repeating signalis not considered to be indicative of any breathing regime. Themagnitude and shape of the repeating pattern can change greatlydepending on posture, device positioning and subject to subjectvariation. For these reasons, embedded algorithms have been selected sothe sensor does not require that the unit be calibrated for anyindividual subject.

FIGS. 12(a) to 12(f) are plots of the main intermediate calculationsfrom an implemented algorithm to determine the respiratory rate for asingle transducer signal, as shown in FIG. 9. FIG. 12(a) shows the rawoutput from a single sensor over a 60 second time period showing thepeaks and troughs indicative of normal breathing. One movement artefactcan be seen as an increase in the signal strength at approximatelysecond 35. After the motion artefact, a short sharp downward artefactcan be seen. FIG. 12(b) shows the same signal with baseline correctionand a moving average smoothing filter applied. The sharp downward spikeis removed from the signal, but the large movement artefact remains.FIG. 12(c) shows the results from an artefact detection function. Wherethe black line is in the higher state, a large non-respiratory artefacthas been determined to have occurred. Other artefact detection methodsmay be overlaid on this as required. FIG. 12(d) shows the same signalwith the section designated as artefact smoothly removed from thewaveform. Small downward troughs can be seen either side of the removedsection. This area is flagged for the following step to ensure it doesnot interfere with the peak trough detection algorithm. FIG. 12(e) showsthe signal in FIG. 12(d) with peaks and troughs identified by thesystem's processor. The area around the detected artefact is removedfrom consideration as it is not an accurate representation of thesignal. FIG. 12(f) shows the frequency spectrum of the signal, with themost prominent signal highlighted at approximately 0.25 Hz, or 15breaths per minute. The smooth removal of the artefact has resulted in aclearly discernable breathing frequency.

FIGS. 13(a) and 13(b) are plots showing examples of two differentbreathing regimes—rib breathing and diaphragm breathing. FIG. 13(a)shows the signals from the two transducers when the subject is standingup and predominantly rib breathing. A short movement artefact is visiblearound second 25. The diaphragm signal is much smaller and less coherentthan the rib signal. Artefact detection will remove the diaphragm signalfrom consideration due to low signal strength. FIG. 12(b) shows a signalfrom the same subject when the subject is lying on their back andpredominantly diaphragm breathing. In this case the rib signal is of lowmagnitude and will be rejected by the algorithm. It is important to notethat these figures show the extremes of rib and diaphragm breathing andthat normal breathing and differences from subject to subject will havea greater or lesser effect on each sensor.

FIGS. 14(a) and 14(b) are plots showing the piezoelectric transducer andaccelerometer signals for a subject sleeping over a period of one hour.Individual breaths are not discernable in FIG. 14(a) at this resolution.The upper and lower magnitudes of the transducers 5 and 6 are shown assolid lines. Transducer 6 is to the fore, and transducer 5 is to therear and shown hatched. The magnitude of the signals can be seen tochange at periods during the hours. Abrupt shifts in the subject's bodyposition can be seen in FIG. 14(b) as jumps in the accelerometersignals, here moving from lying on the hack, to lying on the side andthen back again for the last 20 minutes. The subject can be seen to benominally still for periods of up to 15 minutes between these movements.

The transducers transport the change in voltage through electricalcontacts which have leads connecting the contacts of each movementtransducer to the input electric contacts of the filter circuitry.Filtering circuitry is integrated on a printed circuit board upon whichthe amplifiers and the processor unit reside. All transportation of thesignal from the filter pre-transmission is done on the PCB.

The processor 14 and/or other devices such as GPRS and Bluetooth radiorespiratory sensor is stacked on top of the sensor element which is onthe body. This is secured mechanically and offers easy connection andremoval while ensuring a strong electric connection between both parts.

The preferred relative positions e senor as shown in FIG. 5 on the10^(th) rib is preferred, although the 7^(th) and 8^(th) mayalternatively be used. This placement is the preferred location toutilise the mechanics of respiration. The ribcage, at the denotedlocation, is more flexible and subject to the largest deformationsduring respiratory effort. Where all parts of the thoracic regionundergo fixed loci of displacement, the magnitude of displacement isrelative to individual locations. The fundamental function of thesemechanics is to create a vacuum within the thoracic cavity thus creatingnegative airspace to draw air into the lungs via nose or mouth. This isundertaken through two modes of operation which can be largely mutuallyexclusive.

The distending first operation triggers an involuntary contraction ofthe muscles around the ribcage, causing the rib cage to lift up. As therib cage lifts up, it creates an increased internal volume in thethoracic cavity. This increase in volume also creates a vacuum. Airflows from positive pressure into negative pressure. Thus, air flowsinto the mouth and nose of a human subject and causes respiration tobegin. Air is then pushed out by the muscles around the ribcage whilerelaxing, thus decreasing the internal volume of said cavity and pushingair out of the body. This is also aided by the diaphragm as it maintainsa positive pressure upon the base of the lungs. This diaphragm is amuscle which divides the thoracic region from the abdominal region.

A distending second operation involves an increase in the internalvolume of the abdomen region, which causes a negative pressure and thusdraws down the diaphragm. By causing this, the internal volume of thethoracic region increases, thus creating a vacuum and drawing air in.Air is expelled when the volume of the abdomen cavity is decreased andthe diaphragm is again pushed up against the lungs, decreasing thevolume of the thoracic region and expelling air out.

The effect of the two operations attributed to respiratory effort isseen across the thoracic and abdominal region. It is effective tomeasure respiration at any location using the methodology as outlined bythis invention of a plurality of sensors in a set configuration. Howeverthe preferred location as outlined in this invention is the mostefficient area of measurement.

These two operations can act independently if negligible rib cagemovement is ignored. More often these operations occur in parallel.Thus, to be able to measure both the thoracic and abdominal displacementin a single location is a significant advantage.

Further to the need to detect respiratory rate, the device can alsodetect with high accuracy the moments of inhalation and exhalation asshow in FIG. 12(e), and the duration of each. Such application is highlysought after when monitoring lung capacity to ensure lung damage fromover-pressurising the volume is not exceeded during invasive and/ornon-invasive ventilation.

In embodiments which have one or more accelerometers, these are used todetect when movements occur and this information may be used to smoothor remove artefacts from the strain transducer signals. Artefactcorrection is applied to the strain transducer signal, and the processordoes not assume that all artefacts are accounted for on theaccelerometer—arm movements, direct contact with sensors etc. Also, theprocessor may use accelerometer orientation to weigh the relativeusefulness of the two strain transducers (e.g. weight in favour ofabdomen sensor when patient is lying down.

Some of the advantages of the invention may be summarised as:

-   -   (a) Improved accuracy by ensuring a superior method of sensor        application to the wearer which does not require the wearer's        assistance nor require the wearer to be assisted.    -   (b) By having both filtering and signal processing at the point        of measurement improves accuracy due to reducing anxiety of the        wearer and promoting, longer continuous use, thereby improving        analytics.    -   (c) It also reduces any effects of external influences such as        electromagnetic interference from peripheral devices, unlike the        prior art arrangements having lengthy wires promoting noise in        the signal.    -   (d) Eliminating the majority of unwanted motion artefacts        irrespective of placement within a preferred area of        application.    -   (e) Reducing the effect of philological variances such as body        mass index, body position, location, activity and condition        again pre-processing to ensure high level of accuracy.    -   (f) Having a secure but removable fixing of the sensor and        single construction enables reduction in cross contamination        from device reuse which more efficient utilisation of higher end        electronics.    -   (g) Having a profile and contour promotes easier cleaning.    -   (h) Having profile and contours that promote patient comfort and        reduction from unintentional interference from moving limbs.

The invention is not limited to the embodiments described, but may bevaried in construction and detail. For example the system mayadditionally include a gyroscope and the processor may process thegyroscope output by enabling the posture of the body to be known to theprocessor, thus enabling anomalies of the transducers to be accountedfor.

1. A respiration monitoring system comprising: a flexible substrate, anadhesive arranged on a surface of the flexible substrate to releasablyadhere the flexible substrate to a patient's torso, a plurality ofembedded deformation transducers fixed to said flexible substrateincluding at least a first transducer and a second transducer, the firsttransducer and the second transducer being located on the substrate atan angle relative to a mutual location on the substrate, the firsttransducer and the second transducer having a size and the mutuallocation on the substrate so that simultaneously the first transducer isconfigured to overlie at least part of a patient's 10^(th) rib and thesecond transducer is configured to overlie at least part of a patient's11^(th) rib or abdomen, the transducers being positioned on thesubstrate to enable measuring both thoracic and abdominal displacementin a single location, an electronic controller releasably mounted on thesubstrate, the electronic controller being positioned on a same side ofboth the first transducer and the second transducer, the electroniccontroller receiving signals by conductors from the first transducer andthe second transducer, and an accelerometer producing an output signalrepresentative of a posture of the patient's torso, wherein theelectronic controller is configured to receive signals from the firsttransducer and the second transducer and to compensate for motion noisebased on the output signal from the accelerometer, and to thereby derivean output representative of respiration based upon the signals from thefirst transducer and the second transducer.
 2. The respirationmonitoring system of claim 1, wherein the system comprises a unitarysensor for adhering to a patient's skin, said sensor including: thesubstrate with the deformation transducers, and the electroniccontroller, wherein the electronic controller is included in a housingon the substrate with a signal conditioning circuit, and wherein theelectronic controller housing is releasably mounted on the substrate. 3.The respiration monitoring system of claim 1, wherein the electroniccontroller is configured to trigger an artefact detection algorithm atregular intervals in which signals which are outside predeterminedlimits of measurement are removed.
 4. The respiration monitoring systemof claim 1, wherein the electronic controller is configured to execute,when determining respiration rate, a frequency domain algorithm
 5. Therespiration monitoring system of claim 4, wherein the electroniccontroller is configured to execute the frequency domain algorithm totake accelerometer data from the accelerometer as a secondary input andto compensate for cyclical interference from the subject or environmentsuch as walking, by extracting frequency domain information from theaccelerometer data.
 6. The respiration monitoring system of claim 5,wherein the electronic controller is configured to detect and compensatefor movements using the accelerometer data.
 7. The respirationmonitoring system of claim 6, wherein the electronic controller isconfigured to perform at least one of fall detection, step detection andorientation monitoring using the accelerometer data.
 8. The respirationmonitoring system of claim 1, wherein the electronic controller isconfigured to detect inhalation and exhalation events and monitor lungcapacity.
 9. The respiration monitoring system of claim 1, wherein theelectronic controller is configured to execute, when determiningrespiration rate, a time domain algorithm.
 10. The respirationmonitoring system of claim 9, wherein the electronic controller isconfigured to execute the time domain algorithm to produce a waveformrepresented by a repeating pattern of peaks and troughs at a rateindicative of the respiratory rate of the patient, and detect a distancebetween the peaks and a distance between the troughs in the waveform toderive the respiration rate.
 11. The respiration monitoring system ofclaim 1, wherein the electronic controller is configured to produce awaveform represented by a repeating pattern of peaks and troughs at arate indicative of the respiratory rate of the patient.
 12. Therespiration monitoring system of claim 11, wherein the electroniccontroller is configured to produce the waveform for diagnosis ofdysfunctional breathing events in sleeping subjects by detectingportions of the waveform indicative of a dysfunctional breathing event.13. The respiration monitoring system of claim 1, wherein the electroniccontroller is configured to receive a unique identifier for a use with aparticular subject, and to discontinue or erase said identifier uponremoval of the substrate from the subject and/or re-charging for a nextuse.
 14. The respiration monitoring system of claim 1, wherein the firsttransducer and the second transducer are of equal length, width,thickness and composition.
 15. A respiration monitoring systemcomprising: a flexible substrate, an adhesive arranged on a surface ofthe flexible substrate to releasably adhere the flexible substrate to apatient's torso, a plurality of embedded deformation transducers fixedto said flexible substrate including at least a first transducer and asecond transducer, an accelerometer configured to produce an outputsignal representative of a posture of the patient's torso, and anelectronic controller releasably mounted on the substrate, theelectronic controller configured to receive signals by conductors fromthe first transducer and the second transducer, to compensate for motionnoise based on the output signal from the accelerometer, and to derivean output representative of respiration based upon the signals from thefirst transducer and the second transducer by executing a time domainalgorithm.
 16. The respiration monitoring system of claim 15, whereinthe electronic controller is configured to execute the time domainalgorithm to produce a waveform represented by a repeating pattern ofpeaks and troughs at a rate indicative of the respiratory rate of thepatient, and to detect a distance between the peaks and a distancebetween the troughs in the waveform to derive the respiration rate. 17.The respiration monitoring system of claim 15, wherein the systemcomprises a unitary sensor for adhering to a patient's skin, said sensorincluding: the substrate with the deformation transducers, and theelectronic controller, wherein the electronic controller is included ina housing on the substrate with a signal conditioning circuit, andwherein the electronic controller housing is releasably mounted on thesubstrate.
 18. A respiration monitoring system comprising: a flexiblesubstrate, an adhesive arranged on a surface of the flexible substrateto releasably adhere the flexible substrate to a patient's torso, aplurality of embedded deformation transducers fixed to said flexiblesubstrate including at least a first transducer and a second transducer,an accelerometer configured to produce an output signal representativeof a posture of the patient's torso, and an electronic controllerreleasably mounted on the substrate, the electronic controllerconfigured to receive signals by conductors from the first transducerand the second transducer, to compensate for motion noise based on theoutput signal from the accelerometer, and to derive an outputrepresentative of respiration based upon the signals from the firsttransducer and the second transducer by producing a waveform representedby a repeating pattern of peaks and troughs at a rate indicative of therespiratory rate of the patient.
 19. The respiration monitoring systemof claim 18, wherein the electronic controller is configured to producethe waveform for diagnosis of dysfunctional breathing events in sleepingsubjects by detecting portions of the waveform indicative of adysfunctional breathing event.
 20. The respiration monitoring system ofclaim 18, wherein the system comprises a unitary sensor for adhering toa patient's skin, said sensor including: the substrate with thedeformation transducers, and the electronic controller, wherein theelectronic controller is included in a housing on the substrate with asignal conditioning circuit, and wherein the electronic controllerhousing is releasably mounted on the substrate.